1. Field of the Invention
The present invention relates to a blue light-emitting compound and a display device adopting the light-emitting compound as a color-developing substance.
2. Description of the Related Art
Recent advances in the information and communications industries have increased the need for high performance display devices. Generally, display devices are classified into luminous types and non-luminous types. Luminous type display devices include cathode ray tube (CRT) and light emitting diode (LED), and non-luminous type display device include liquid crystal display (LCD).
As an index of the basic performance of the display device, there are operating voltage, power consumption, luminance, contrast, response time, life span and display color, among others.
The LCD, as one of the non-luminous type display device, has been most favored recently, due to its light weight and low power consumption. However, characteristics such as response time, contrast and viewing angle properties are unsatisfactory, leaving room for improvement. Meanwhile, an electro-luminescence (EL) device has been focused as a next generation display device which can solve such problems.
The EL device as a spontaneous luminous type display has a broad viewing angle, a good contrast characteristic and a rapid response time. The EL device is classified into an inorganic EL device and an organic EL device depending on the material used for a light-emitting layer. In particular, the organic EL device has good luminance, driving voltage and response time characteristic and can display a multitude of colors, compared to the inorganic EL device.
FIG. 1 is a section view showing the structure of a general EL device. Referring to FIG. 1, an anode 12 is formed on a substrate 11. A hole transport layer 13, a light-emitting layer 14, an electron transport layer 15, and a cathode 16 are formed on the anode 12 in sequence. Here, the hole transport layer 13, the light-emitting layer 14 and the electron transport layer 15 are organic thin films formed of an organic compound.
The organic EL device having the above structure operates based on the following operation principle. When a voltage is applied between the anode 12 and the cathode 16, holes injected from the anode 12 move through the hole transport layer 13 to the light-emitting layer 14. Meanwhile, electrons are injected from the cathode 16 through the electron transport layer 15 to the light-emitting layer 14. Also, carriers are recoupled in the light-emitting layer 14 to generate excitons. The excitons are transited from an excited state to a ground state, so that fluorescent molecules of the light-emitting layer emit light to form a picture.
Also, an organic EL device adopting an aromatic diamine and aluminum complex having a low molecular weight has been developed by Eastman Kodak Company.(Appl. Phys. Lett. 51, 913, 1987)
In addition, an organic EL device adopting a polymer such as poly(p-phenylenevinylene) (PPV) or poly(2-methoxy-5-(2xe2x80x2-ethylhexyloxy)-1,4-phenylenevinylene) as a material for a light-emitting layer has been disclosed (Nature, 347, 539, 1990, and Appli. Phys. Lett. 58, 1982, 1991). However, PPV among the polymers has a poor solubility in an organic solvent, so that it is difficult to adopt a spin-coating so as to form a film by spin-coating method. To solve this problem, a soluble PPV having a functional group capable of improving its solubility in an organic solvent has been developed. The organic EL device having a light-emitting layer formed of PPV or a derivative of the PPV displays a multitude of colors from green to orange.
Also, the well-known blue light-emitting compound is low in luminous efficiency compared to another color of light-emitting compound, thus a need for a new blue light-emitting compound having a high luminous efficiency has increased.
Accordingly, a compound having a non-conjugative spacer group such as silicon (Si) or oxygen (O) between luminous groups of PPV, as a blue light-emitting compound, has been suggested. However, a light-emitting layer formed of the light-emitting compounds is not satisfactory in characteristics such as a film strength.
It is an object of the present invention to provide a new blue light-emitting compound capable of solving the problems.
It is another object of the present invention to provide a display device adopting the blue light-emitting compound as a color-developing substance.
To achieve the first object of the present invention, there is provided a light-emitting compound represented by the chemical formula (1): 
wherein Ar1, Ar2, and Ar4 are independently selected from the group consisting of chemical bond, unsubstituted or substituted phenyl, unsubstituted or substituted naphthalene, unsubstituted or substituted anthracene, unsubstituted or substituted diphenylanthracene, unsubstituted or substituted phenanthrene,. unsubstituted or substituted indene, unsubstituted or substituted acenaphtene, unsubstituted or substituted biphenyl, unsubstituted or substituted fluorene, unsubstituted or substituted carbazole, unsubstituted or substituted thiophene, unsubstituted or substituted pyridine, unsubstituted or substituted oxadiazole, unsubstituted or substituted oxazole, unsubstituted or substituted triazole, unsubstituted or substituted benzothiophene, unsubstituted or substituted dibenzofuran, and unsubstituted or substituted thiadiazole; Ar3, unsubstituted or substituted fused aromatic ring, is selected from the group consisting of unsubstituted or substituted naphthalene, unsubstituted or substituted anthracene, unsubstituted or substituted diphenylanthracene, unsubstituted or substituted phenanthrene, unsubstituted or substituted indene, unsubstituted or substituted acenaphthene, unsubstituted or substituted fluorene, unsubstituted or substituted carbazole, unsubstituted or substituted benzothiophene, and unsubstituted or substituted dibenzofuran; R1, R2, R3 and R4 are independently selected from the group consisting of hydrogen, ethyleneoxy group, C1-C20 alkyl group, C1-C20 alkoxy group, aryl group, trimethylsilyl group, and trimethylsilylaryl group; k and m are independently 0 or 1; and n is an integer from 10 to 200.
The second object of the present invention is achieved by a display device adopting the light-emitting compounds as a color-developing substance. Preferably, the display device is an organic electro-luminescence (EL) device adopting the light-emitting compounds as a color-developing substance.
To achieve the second object of the present invention, there is provided an organic electro-luminescence device comprising an organic layer between a pair of electrodes, wherein the organic layer comprises a light-emitting compound represented by the chemical formula (1): 
wherein Ar1, Ar2, and Ar4 are independently selected from the group consisting of chemical bond, unsubstituted or substituted phenyl, unsubstituted or substituted naphthalene, unsubstituted or substituted anthracene, unsubstituted or substituted diphenylanthracene, unsubstituted or substituted phenanthrene, unsubstituted or substituted indene, unsubstituted or substituted acenaphthene, unsubstituted or substituted biphenyl, unsubstituted or substituted fluorene, unsubstituted or substituted carbazole, unsubstituted or substituted thiophene, unsubstituted or substituted pyridine, unsubstituted or substituted oxadiazole, unsubstituted or substituted oxazole, unsubstituted or substituted triazole, unsubstituted or substituted benzothiophene, unsubstituted or substituted dibenzofuran, and unsubstituted or substituted thiadiazole; Ar3, unsubstituted or substituted fused aromatic ring, is selected from the group consisting of unsubstituted or substituted naphthalene, unsubstituted or substituted anthracene, unsubstituted or substituted diphenylanthracene, unsubstituted or substituted phenanthrene, unsubstituted or substituted indene, unsubstituted or substituted acenaphthene, unsubstituted or substituted fluorene, unsubstituted or substituted carbazole, unsubstituted or substituted benzothiophene, and unsubstituted or substituted dibenzofuran; R1, R2, R3 and R4 are independently selected from the group consisting of hydrogen, ethyleneoxy group, C1-C20 alkyl group, C1-C20 alkoxy group, aryl group, trimethylsilyl group, and trimethylsilylaryl group; k and m are independently 0 or 1; and n is an integer from 10 to 200.